1. Field of the Invention
The present invention relates to a semiconductor pressure sensor and, particularly, to a semiconductor pressure sensor used in automobiles or the like.
2. Description of the Related Art
FIG. 4 is a sectional side view illustrating a conventional hollow package type semiconductor pressure sensor. In FIG. 4, a semiconductor pressure sensor chip 1 having a gage resistance (not shown) thereon is bonded to a pedestal, for example, a glass pedestal 2. The glass pedestal 2 is mounted on a die pad 3 by using, for example, a resin adhesive 8a. The die pad 3 is a portion of a lead frame (not shown) which is also provided with outer leads 4. The die pad 3 is fixed to the bottom of a package base 6 by an adhesive 8b so that the semiconductor pressure sensor chip 1, the glass pedestal 2 and the die pad 3 are contained in the package base 6.
The outer leads 4 of the lead frame, which is integral with the die pad 3, are fixed to the upper end of the package base 6 by an adhesive 8c. A package cap 7 which has an opening 7a to form a hollow portion is also fixed to the upper end of the package base 6 by an adhesive 8d so as to cover the semiconductor pressure sensor chip 1 to form a package. The inner portions of the outer leads 4 are electrically connected to electrodes (not shown) formed on the semiconductor pressure sensor chip 1 by wires 5 serving as electrical connection means. The package base 6 and the package cap 7, for example, are made of an epoxy resin.
In the conventional semiconductor pressure sensor constructed as described above, a diaphragm region 1a in the semiconductor pressure sensor chip 1 serves as a vacuum chamber when the semiconductor pressure sensor chip 1 is bonded to the glass pedestal 2 in a vacuum by, for example, anodic bonding. When the vacuum chamber is at a reference pressure, and when outer pressure is applied to the surface of the semiconductor pressure sensor chip 1 from the opening 7a of the package cap 7, the thin diaphragm is distorted, and the value of the gage resistance (not shown) on the semiconductor pressure sensor chip 1 is changed by the piezoresistance effect and generates an output signal corresponding to the pressure in a bridge circuit comprising the gage resistance. The generated output signal is output from the outer leads 4 through the wires 5.
In the aforementioned semiconductor pressure sensor, the ends 4a of the outer leads are cantilevered and not fixed within the package. There is thus the problem that when vibration is applied to the semiconductor pressure sensor mounted on an automobile or the like, the ends 4a resonate, and the wires 5 bonded to the ends 4a are detached due to vibration. Although the inner leads can be shortened for preventing the problem, undesirable interference such as contact between the wires 5 and the adhesive 8d occurs when the package base 6 and the package cap 7 are bonded to the outer leads 4. It is thus impossible to prevent the wires 5 from being detached due to vibration.